Transcript Revision Exam Questions - Particle Physics Group

P1Y Quantum Phenomena
Question Revision
• Atomic
– Question sheet 1-7, 6
• Particle Physics
– Question sheet 8-12, 11
• Cosmology
– Question sheet 13-16, 15
• Last May’s exam:
• Anti-Hydrogen (atomic + particle physics)
• b anti-b quark production at LEP
Exam hints
• Answer five questions
– Twenty five minutes per question
– If you attempt more than five, indicate your best five
• Including one from each section
– Extra section for P1Y* candidates
• So, you must answer either one or two from
quantum section.
• Choose your questions carefully
– Spend 5 minutes reading through
– Look at the mark allocation for each bit of the question.
– Don’t waste time
• e.g. last years’ paper had a question which required a graph.
• Some students clearly wasted time drawing perfect graphs.
• The plotting of the graph, line, and axis labelling was only
worth 2 marks
Marking
• No negative marking
– In practice we will mark all questions you’ve done and
give you the best mark we can!
– We also mark work you crossed out, as long as we can
still read it!
• Explain what you are doing.
– E.g. spectroscopic notation for Argon
– (1s22s22p63s23p6) [3] If you write down
• fill electron levels in order
• Fill all n,l,m states l<n m=-l,…,+l
You’d get 1.5
• Make your working/ rough work readable
• If your numerical answer is physically unrealistic
say that you realised this.
May 2003
Cold Anti-Hydrogen was produced for the first time at CERN in 2002.
(i) What is anti-hydrogen and what fundamental particles does it
consist of ?
{4}
(ii) An anti-hydrogen atom is in an excited state with an energy
 13.6
eV
2
4
Describe the quantum numbers of the atom and list the possible atomic
states.
{6}
(iii) An anti-hydrogen atom hits the wall of a vessel containing it.
We observe several pions and a few ns later two photons.
Describe what happened, estimating the sum of the energy of all the
observed particles.
{6}
[proton/neutron mass 940 MeV, electron mass 0.5MeV ]
May 2003
An electron-positron collider is operated with beam energies of 45.5 GeV each.
(i) Draw the lowest order electromagnetic and weak interaction Feynman diagrams for
production of a b anti-b quark pair in this collider.
{4}
(ii) Calculate how far does a b quark travels before decaying.
{4}
(iii) Draw one example Feynman diagram for the decay of the b quark.
{3}
(iv) Describe what is observed in the particle physics detector
{5}
[mass of b quark 5GeV, lifetime 1.5ps]